Imagine you have a box full of Uranium-235 atoms 🔭

Imagine you have a box full of Uranium-235 atoms.

Eventually, the Uranium atoms will all turn into Lead, but they're not in any hurry to do this.
If you want to wait until half your Uranium atoms have turn into Lead, you'll be waiting 700 million years.
Radioactivity involves more than just beta decay.
There's actually more going on here.
But the point is that beta decay can be a slow process and it's a random process.
Now we finally have covered enough background to explain how the Sun shines.
This was worked out in the 30s by Hans Bethe.
The Sun is mostly made of Hydrogen-1 which is just a proton.