Not necessarily. That mostly has to do with weight. If you have a heavy reel mower, pushing it up an incline will be tiring, and the mower won’t perform to its fullest. It is not that the mower “can’t handle it”, it’s just that it can’t perform as well as it normally could that way. That does not mean that all lightweight mowers can handles inclines, however. Read up on the mower to know definitely.