Do not allow someone to question your determination.
No one has the right to.
If you have the competency to do and/or accomplish something, you can achieve it with patience, hard work, focus, faith, trust, and of course, determination. Always believe. No one has the right to tear you down.
And if they have the audacity to do it, leave them alone. Expose what you can do and respect their perspective towards you. This world is full of people who’ll dislike something or someone especially when it is not reasonable or logical.