Diagnose Why My DIY Project Went Wrong

Something's not right. The door binds, the joint's gappy, the finish is patchy, and you're about to start ripping bits out on a guess. Describe what you built, the problem, and what you've already tried. It diagnoses the likely root cause ranked by odds, gives you a quick test to confirm before you commit, then the repair steps.

My DIY project has a problem. Here is what I built: {WHAT_I_BUILT}. Here is the problem I am experiencing: {PROBLEM_DESCRIPTION}. Here is what I have already tried: {ATTEMPTED_FIXES}. Act as an experienced tradesperson and diagnose the most likely root cause. Give me: (1) the probable cause ranked by likelihood, (2) a quick diagnostic test I can do to confirm the cause before committing to a fix, (3) the repair steps for the most likely cause, and (4) how to prevent this issue on future projects. Avoid jargon; explain as if talking to someone with basic DIY experience.