There is a thin line between confidence and overconfidence.
"I can do this." is confidence.
"Only I can do this." is overconfidence.
There is no harm in building yourself. Learn the skills. Take one step every day to become a better version of yourself. The problem arrives when you assume there is no other person who can do your job.
Excellence is not a destination; it's a journey. James Altucher’s 10,000-hour rule is a golden way to improve every aspect of your life. But what you must avoid is degrading other people.
In Islam, ALLAH teaches us to stay humble. To succeed, you must do whatever you can and leave the rest to ALLAH. Make your effort and pray to GOD for a better ending.
How to stay humble?
Do two things:
Be grateful
The more thankful you become, the more GOD will bless you. And being grateful indicates that you're only the messenger. The ultimate power comes from ALLAH, and you're just blessed to use it.
Every morning count down 10 things that you're grateful for. Repeat the exercise last time before you sleep.
Pray a lot
Prayer does wonders. Pray with a sincere heart and a humble soul, and GOD will bless you with the confidence you need.
Closing thought
In the end, it's all bout doing whatever you can and staying humble about it. The more humble you become, the more GOD will bless you.
Till next time, take care!!