Batsman error is a curious concept. It's what all bowlers are looking to cause when they turn at the top of their mark, by applying sufficient pressure to force the fatal misjudgement, or by setting a crafty trap and springing it on the unwitting. Because, as Jack Leach finally proved with an outstanding delivery late in the day to Kusal Mendis, it's only a glorious handful of balls that are genuinely unplayable.
So what are we to make of the batsman errors in this contest so far? Specifically the Sri Lankan ones, for England, despite an afternoon of rather harder toil than they might have envisaged after the first innings, still have the first Test at their mercy, with a hefty lead in the bank and two more days on a wearing deck to reassert their authority.
But even in the midst of an otherwise valiant rearguard, the one wicket to fall in the first 59 overs of Sri Lanka's second innings was another self-inflicted wound of the type that came in a torrent on day one. With only one man back on the rope at deep backward point, even England's unofficial Maker of Things to Happen, Sam Curran, struggled to take the credit for a wide outswinging long-hop to a well-set Kusal Perera, and his coy puff of the cheeks as Leach completed the catch rather gave the game away.
"You don't take Test wickets for granted but, yeah, that wasn't the way I expected," Curran said at the close. "The way things happened for us on day one aren't going to happen very often, but you don't take those days for granted because when they do come you've got to enjoy them. In the second innings, Sri Lanka fought really hard, which we expected, but we stuck in there as a bowling group, keeping the scoring rate as low as possible in really tough conditions."
To be fair to Perera, his second-innings dismissal was not remotely as culpable a dismissal as his first-day aberration - a second-ball reverse sweep to Dom Bess that set in motion one of the most preposterous five-wicket hauls in Test history. However, it was in keeping with a contest in which England have so far claimed just three wickets out of 13 with good deliveries, and the first two of those might well have been resisted by less skittish opponents.
There was Stuart Broad's legcutter to Mendis, an outstanding piece of thinking against an opponent who at that stage had not scored a run in four innings, but it still required a nervy hard-handed thrust to seal the deal. As for Dilruwan Perera, his second-ball inside-out drive against Bess was perhaps not the ideal response to a well-flighted delivery on off stump.
In mitigation for England, this match is effectively their warm-up fixture, because a low-key intra-squad warm-up in Hambantota wasn't nearly enough of a gallop after nearly five months in mothballs for most of the squad. But with five more Tests to come in the next two months, including four against a ferociously drilled India who are currently dredging new reserves of spirit on their tour of Australia, the worry for Joe Root's men is that they might not find the freebies quite so easy to come by from here on in.
"No-one's really played much cricket so you'd expect a bit of rustiness and a lack of rhythm, but the guys fought hard in humid, sweaty, hot conditions," Curran said. "The build-up was what it was, we have no complaints. Rooty was very clear that we need to hit the ground running which we luckily did on day one. But day four is going to be a test for us, because we've got a lot of overs in our legs now, and we've got to come back and keep fighting."
And for that reason, it's hard to pick too many holes in a team who are still favourites to complete an unprecedented fourth consecutive victory in Asia - all of them in Sri Lanka, following their 3-0 clean sweep two winters ago.
They've got some significant bench-strength to come as well - for the India leg of the winter, if not before - including James Anderson, who seemed the pick of the bowlers in Hambantota, as well as Ben Stokes and Jofra Archer, two men whose methods might prove especially effective in Asia, not to mention Moeen Ali - now finally released from his Covid quarantine.
However, the likelihood of Moeen returning for the second Test is slim, given both his own lack of match practice, but also the fact that Leach and Bess are now finally getting enough overs themselves to start feeling a hint of rhythm. Leach in particular - one of the stars of that last Sri Lanka campaign - had bowled a grand total of 52 first-class overs in the 12 months leading up to this Test, through a combination of illness and life in the England bubble. It's little wonder he has needed a session or two to locate his range.
"Line, length, pace … everything really! I probably came up a little short," Leach told Sky Sports at the close. "I've been short of match overs for a little bit of time. You can do as much as you want in the nets but you need that stuff in games. I found I bowled a little bit short when I tried to bowl quicker, that's something to think about for tomorrow."
The good news for England is that their game plans, though lacking the requisite meat on the bone, do seem to be firmly in place. In particular, the use of Mark Wood in a series of two- and three-over bursts has been encouraging - and the fierce lifter that slammed into Perera's top hand was an early example of the shock value of a raw quick, even on an unconducive deck.
At the other end, Stuart Broad produced another inventive and economical display of out-of-the-box seam bowling - showing echoes of Darren Gough's methods from his triumphant tour of 2000-01, going through the wall, round the wall, sometimes even under the wall with an attempted slow yorker to Lahiru Thirimanne late in his second spell, in a bid to prise a rare and precious opening.
However, Broad was blowing by the end of his eighth over, and sixth maiden - a state of affairs that reiterated the importance of England's spinners. It's all very well inverting the pyramid and turning to your seamers to bowl the spinners' holding overs, which was a secret of England's success here two years ago, but it does increase the onus on those spinners to attack with the utmost discipline.
Instead, Bess in particular found his good fortune from the first innings being rebalanced in a leaky display, while Leach's own struggles seemed to have been summed up in his 16th over, when Mendis propped forward to a decent biting delivery and lobbed a simple chance to short leg. Sadly for England, however, that fielder only materialised one ball later - Leach's economy rate of close to four an over had rather negated the option of being attacking.
But late in the day, Leach found his fizz at last, and with a nightwatchman at the crease alongside the steadfast Thirimanne, Root remains confident that his side is on course to close out the contest.
"When you come and play here, and at this ground in particular, you've got to remember how quickly things can change, and how difficult it can be to start your innings," Root said at close, after establishing England's dominance with his magnificent 228.
"It's really important as a bowling group that we remember that. You've got to make those first 10-15 balls count against a new batter, and remember you're always in the game throughout, because there's always that one ball somewhere if you get it in the right spot and fortune's on your side.
"You've just got to work hard and try and be as patient as possible, and keep applying as much pressure as you can for long periods."
Andrew Miller is UK editor of ESPNcricinfo. He tweets at @miller_cricket