achievable
Possible to reach or finish if you work for it.
Achievable means possible to accomplish or reach through effort and realistic planning. When a goal is achievable, you have a genuine chance of making it happen if you work at it. It's the sweet spot between too easy (which wouldn't teach you much) and impossible (which would just frustrate you).
A teacher might help you set achievable goals for the school year: reading 20 books is achievable, reading 2,000 probably isn't. Training to run a 5K race in three months is achievable for most people, but qualifying for the Olympics in that same timeframe isn't. An achievable project deadline gives you enough time to do good work without rushing, but not so much time that you put it off.
The key is whether the path from where you are to where you want to be is realistic. Achievable doesn't mean easy. Learning to play a song on the piano is achievable, but it takes practice. Building a treehouse is achievable, but it requires tools, materials, and help. When you break big dreams into smaller, achievable steps, you turn distant wishes into actual accomplishments.