My feet naturally turn in at the toes. Since I was about 10yo I have made a conscious effort to stand and walk with my feet pointing straight.
I'm now 50 and am developing problems with my knees. Partly, I know, because I have fallen arches (I use orthotics) and partly from an injury 30y ago. But I have noticed that my knees are less uncomfortable if I let my toes turn in.
Have I been doing myself damage by keeping my feet in an 'un-natural' position? Straight feet feel natural to me now, but they revert to turned-in when I am particularly tired.