With some of my knots failing when in use, I sat down with spools of mono and fluorocarbon in various sizes and tried tying and testing to destruction the knots I was using, plus a couple of new ones.
I found that very educational, and changed the knots I was using accordingly (ie I now use different knots for attaching the fly according to whether I'm using mono or flurocarbon, and have stopped using a couple of knots often recommended for joining lengths of line (tippet to leader).
When fishing, I now always test any knot tied quite robustly, both just after tying and at the start of each session or following the landing of a fish etc, and test the whole rig by hooking it to the landing net mesh and lifting against the weight of my foot on the net.
Since then, I haven't lost a single fish, despite some savage takes (the lake I fish has some seriously big fish).
Oh! And I've learned to keep my rod at right-angles to the retrieve so that when a smash-take occurs, the rod can absorb the sudden and unexpected force.
I now have a lot more confidence in my rig, and one less worry on my mind when fishing