A good position can disappear through moves that each seemed individually harmless.

Decline rarely arrives as one obvious mistake. It comes as a run of small concessions, each defensible on the day it was made, which together give away the ground you were standing on. Because no step felt like the step, there is nothing to point at afterwards. Small moves never set off the alarm a large one would.

Every so often, look at the whole position rather than only the next decision. Ask whether you would have accepted where you are now if it had been offered in one go. If the answer is no, the next small move is the one to argue with.