Watch this movie for the probable solution.

When you trim a clip, there is (usually) "extra" media before and after the part of the clip you want in your timeline. (That’s what trimming does, allows you to select a portion of a clip that will show in your movie)

COOL TIP: If you select the Slip tool by pressing "S", and click on a clip in the timeline, you’ll see a brown outline showing you the extra media on either side of your "trimmed" clip.

Another way to see what handles are on your clip is by double clicking it, then noticing how much footage lies on either side of your in and out marks.

When you add a transition between clip #1 and clip #2, FCP uses the media AFTER clip #1 to dissolve (or whatever) into the media BEFORE clip #2.

If there is no extra media after clip #1 or no extra media before clip #2, then your transition will be only 1 frame long! (Or give you the error message "Insufficient content for edit")

Solution: always capture more of a clip than you’re going to use- "trim" the clip in the Viewer by setting in and out points.

Another cool tip: If you haven’t got it yet, our Final Cut Pro Foundations course has a lot of info on this topic- and all others!