We try our best to make sure that the stopping point is clear. Often times it will be checkmate or a decisive material advantage. Problems can also end with a pending overwhelming attack or massive positional advantage. Occassionally problems will end with stalemate or return to material equality (if the position warrants it).
If you are unsure of the results, you can click on the "Analysis" button on the right hand side of the Tactics Trainer to analyze the position more closely.
keywords: tactics problem length end stop why