If it is achievable, it can be done. When setting goals for yourself it is critical that you honestly assess whether or not they are achievable, otherwise you are doomed to failure.
If you achieve something, it must have been achievable. Things that are considered achievements usually require some dedication, skill, perseverance or intelligence. Things that may or may not be achievable, or possible, include solving global warming and world hunger. If you want to fly to the Sun on homemade wings, check with Icarus on whether or not that’s achievable.