[DTD]

I don't play long sessions and get a bit annoyed if I make one clear mistake in a big pot per session. Most people can at least justify any play they make though so if you are looking at blantant errors that are hugely -EV then you are often just looking at tilty moves. In terms of "general" bad plays, without it having to be a big hand and including missed value bets for example, then we all make loads I guess.

It's possible just to have the wrong mindset, like being too passive and just not in the mood for a battle, and play badly (compared to the norm) for a whole session. In that case your expected gain is likely to be way less than normal, but there may not be any obvious bad errors as such.