The fun thing about traveling at near light speeds is: the greater the velocity difference between you and something is, the more massive that something seems to you (at least if relativity is to be believed). For example, if you’re traveling 239,833,966.4 m/s (0.8c) faster then something else, everything else’s mass will have increased by two thirds. If this increases to 269,813,212.2 m/s (0.9c), the mass increase will have jumped to almost one and a half. The faster you go, the greater this increase is.
This means that if you’re traveling at 299,792,457.7 m/s (0.999999999c) a gram of spacedust will effectively mass over 22 kg and strike you with the force of 6,596,434,069 N. That’s a lot of newtons, concentrated on a point the size of a pinhead. This will punch a hole through pretty much any substance we know of, and there’s a lot of spacedust out there. Building spaceships isn’t easy.
See, the little things in life do matter.
Also a term used by people (Ok… really I’m the only one) to refer to that which seems harmless, but isn’t.