My grifter went through phases of having three, one, or no gears at all. No gears usually happened during the summer traffic light races after school, when the damn thing would give under maximum effort and dump me unceremoniously on the top tube, to be followed by about 10 minutes of writhing around on the ground. I would sometimes then have it jammed on 2nd by tying the gear selector thing at the hub back to the frame, or just ride it everywhere in third all the time.
I think this is why I have a predeliction for ss ht these days. Knees seem fine so far.