I've done that too! LOL I have one machine that threads left to right and one that threads right to left, the other two thread front to back. If it's been a while since I've sewn on one I pull out the manual to remind myself which way to the thread goes.
My most frequent DUH! moment happens when I'm FMQing---everything is zipping along nicely, stitches are looking pretty, and then that oops moment occurs when I realize I've forgotten to lower my presser foot---it's amazing how nice the stitches on top can look while there's a rat's nest forming on the bottom--the problem here is, that my main quilting machine doesn't seem to mind at all, so I can get quite a large area quilted before I realize there's a problem
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