A good team, important/strategic partnerships, good marketing and actually delivering on the project's promises is almost guaranteed to make such projects a big success
These are needed but not limited to. It means just because of having all these will not guarantee big success for a coin. Have seen many good concept based coins got failed due to lack of supporters. It means devs must work on convincing new investors all the times. If a project fails to attract new investors then it may get heavily dumped and the slowly will get delisted from exchanges.
When a project remain attractive for new investors and for existing investors to keep holding their coins/tokens?
It will remain attractive when new features being added and roadmaps is getting updated regularly and when devs interact with crypto community in social media etc.
Overall, active dev team is the most important requirement for success of a coin.