There is always evidence you can point to that indirectly shows the existence of a loan. For example, if the other person is denying that you gave them the money, then where did the $10,000 come from so quickly? Are there any text messages, email correspondence, etc. that record parts of the loan agreement? When you met to give this person the money, were there any witnesses around? Have they been repaying you? Any evidence that corroborates (i) the existence of a loan between the two of you; and (ii) the terms of the loan that you are alleging, will help and be useful.
It is never a good idea to hand over money without any written record of it. However, you need to look at all the evidence you have. If you have absolutely no evidence whatsoever, then you probably already know that you have little chance of getting it back in court. In this case, you will need to hope that this person is honest and will repay you.