Minecraft wiki entry for Redstone_components, associated text: When a sticky piston is activated by a pulse shorter than 1.5 ticks, it pushes the block in front of it, but fails to pull back the pushed block on the end of the pulse. If that sticky piston is activated again by any pulse, it can still pull back the block. Thus, a sticky piston running on fast pulses (for example, 1-tick pulses) pushes and pulls a block every other pulse.
A piston is a transparent block, so powering it directly does not cause adjacent mechanism components (including other pistons) to activate (for exceptions see Quasi-Connectivity above).