In my language, when there is a capable or malicious or any other person who is potentialy able to do something ("usually" a negative act), but they just don't have the needed requirements to do what they want, or the situation is not so good that it should be to make them able to perform their desired act, we say metaphorically:
- He's a good swimmer, just lacks a swimming pool (water) [which I think literally it's quite clear in meaning]
The only close concept I found in a translation web page was:
- He / she just lacks sunshine to make the hay!
- He / she just lacks a hay!
How would you normally describe such a person/situiation in English using an expression/saying?