There's an old video editor saying that goes: "If you can't solve it, dissolve it."

Meaning that if you're having a challenging time making a cut between two shots or two scenes work, just put in a dissolve.

Obviously, that saying is a rather glib and amusing phrase, as the judicious use of dissolves can be a very effective visual tool in film making.

This video by Kevin B. Lee, entitled The Art of the Dissolve, showcases some examples of dissolves from movies of the past and present.