"External interfaces don't portray internal mechanisms"

Though this seems self explanatory it does take a while to understand what it actually means. So thoughts on this topic are always welcome i feel. There are some kannada equivalents to this too - " Bellagiruvudella Hallalla" ( Everything white is not Milk ), "Mukhanodi marhogbeda" (don't go by the looks etc). Basically all this means be careful before you take any step and just dont go by looks.

Since a software programmer may better understand the term "interface" i thought this will be be a good one for them.