A lesson I was taught awhile ago was "if you trust someone, and they speak from a non emotional spot, maybe you can trust them". I used to always have performance anxiety when it comes to the bedroom and my tools wouldn't operate correctly. I used to think I was a complete useless POS when I would be too quick. Seriously the thoughts in my brain were "she is sick of you" "she won't talk to you again" "you will never be able to satisfy a girl" and so on. Really painful thoughts and I believed them for a long time. So much of this thinking changed when I was with a girl, busted very quick and got super emotional. So emotional that I was starting to spiral down a very dark thought loop. She saved me by saying "hey, it's okay. It's really not a big deal". Of course initially it didn't land when she said that, just like what your dad or your friend says about your career. So I kept resisting her words but it got to a point where she said "you're listening to your thoughts In a emotional perspective, can you trust me?" "Can you trust me?" "Yes" "Okay, well it's not a big deal, I still love you the same" And I had a bit of release from self defeating thought from that that led to me seeing the situation more correctly over time. All I'm saying with this, is maybe your dad and friend see your stutter from a non emotional standpoint where they can actually correctly judge the impact it has externally. But you're facing the internal demons and stories you have created of why youre not enough. Of course you will limit your capabilities from that standpoint. Maybe you just need to trust them and go after what you truly want. All in the way, when going after what you want, the doubts will start to fall off when you realize how capable you actually are.