For example, try to draw the character 口 on the 'draw' functionality on jisho.com -- the correct stroke order is (cardinal directions for 3 strokes): 1. NW -> SW 2. NW -> NE -> SE 3. SW -> SE. If you try to do it any other way it will fail.
If this is a problem for you (e.g. learning Japanese and don't know stroke orders and/or don't care to learn them exactly) -- the Google Translate handwriting input for Japanese does not have this behavior (or at least as much) and will effectively recognize your incredibly shittily reproduced kanji.