Because O is bigger than N and our space is limited, we all try to fit 40 lbs. of stuff in a 10 lb. box.
TR-18 has the right idea. Reverse ("S") curves are trouble, both in 1:1 and 1:48. The sharper the curves and the closer their proximity, the more troublesome. Trains on track are very much like string on a table, pull the string and it straightens out; push the string and... well, you know. Try to push string around reverse curves and the results are predictable.
Good luck.