In engineering, a common measure of reliability is the mean time between failures, or MTBF. What this means, basically, is how long the product runs without failing, on average. Obviously, the longer it goes without failing, the more reliable the product is. Software that runs continuously for weeks or months is better than software that fails every few days.
But if the software could be made to run faster, it might fail more often, because it gets to those failure points in less time. In other words, the faster software has a lower MTBF, and is therefore less reliable.
And upgrading the computer hardware, by adding more memory, more disk space, etc., is apt to improve the software's performance which will, in turn, reduce the MTBF.
So upgrading your computer will make your software worse!