Seams coming apart - some causes
 

Usually my seams do not come apart - any more -

Some things that have caused problems for me:

The seam allowance got too skimpy!!! It really is better to unsew the seam and sew it again properly.

The fabric was a frayer and/or flimsy.

The fabric was very loosely woven.

Using an overly long stitch length.

I was trying to "fudge" a skimpy piece to fit - and that resulted in a skimpy seam allowance - and that resulted in the seam pulling apart.

The fabric gave up after being unsewn and resewn several times.

When strip piecing, did not shorten the stitch length, so the units came apart before I got around to incorporating them into bigger units.

Not stay-stitching around the outer edge of a pieced border.

This is the one that catches me. I often don't use borders at all so I have to watch for things coming apart. If I'm being smart I put lock stitches on the ends of the seams that I know are going to be left at the edge, but that's not always practical and I don't always remember to do it when it is. I've had to go and hand-stitch things back together because it'll already be quilted and I don't notice they're coming apart until I'm getting ready to put on binding. I usually use a dot of fray check on the original seam when that happens.

Yep. Skimpy seam allowances is a common problem for me.

a really hot iron and some poly threads = the case of the disappearing seams..

Isn't it a great feeling to know you are really progressing with techniques and skills? Well done!

When I have a skimpy seam, I go back and add another stitching line next to the skimpy part to reinforce it. I also have pulling apart when I chain piece and the thread in-between is barely enough to cut apart, so I need to remember to use a shorter stitch length.