the major problem of Bitcoin is probably lack of adoption.
and the main reasons of lack of adoption are probably ease of use and insufficient security

Software development team here.
We would like to hear from the community what are the most annoying\frustrating stuff you have with Bitcoin and would love to get a solution for ?
Feel free to talk about any problem, even if it seems unsolvable or too abstract (e.g. Bitcoin is not safe enough for the average user)
Edit:
After reading all the replies, I feel confident summarizing that the #1 problem of Bitcoin is probably lack of adoption.
And the main reasons of lack of adoption are probably ease of use and insufficient security.
We are a team of entrepreneurs and software developers that are going to spend the next following months-year on developing a new product.
One of the most appealing markets for us is the Bitcoin market.
We will try to learn us much as possible from your replies and try to tackle the problems head on.