It is very difficult to understand when Bangladesh batsmen perform well and when they perform poorly. Same opponent, same wicket conditions, but Bangladesh's performance in the two matches was different. In the first Test match, Bangladesh batted well in 2 innings, on the contrary, Sri Lanka batted similarly to Bangladesh, due to which the result of the first Test match was drawn, but when Bangladesh came out to play the second Test match, we noticed Bangladesh's bad batting from the first innings. Due to this bad batting of Bangladesh, Bangladesh lost to Sri Lanka by an innings.
When a team loses to another team by an innings in one or more matches of a Test series, it seems that one team is very strong in Test cricket and the other team is quite weak in Test cricket. Although Bangladesh and Sri Lanka are in the same category of teams in Test cricket, Sri Lanka is much ahead of Bangladesh in terms of consistent performance.
It depends upon the match conditions and also if some of the players play well, then the other players will automatically get the confidence, but if the team is losing wickets, then you will find none of the batsmen will be able to see the form or partnerships.
Anyway, what happened in this match is history now. The worst they can do is to keep this defeat in mind and that can affect their play in the upcoming ODI and T20 series. The Bangladesh team should forget this defeat and should try to win the ODI series and this is the best possible revenge they can take from Sri Lanka.