One problem with the IRR method is that:

it does not take account of cash flows over a projects full life.

it does not take account of the cash outflows.

it does not provide a rate of return.

it values a dollar received today the same as a dollar that will not be received until sometime in the future.

it assumes that the cash flows generated by a project can be reinvested back into the same project, and this assumption is often not valid.