But after I have eaten the burger I have nothing left.
I think of it more like buying a house for 20k and investing 100k in it. Now its hopefully worth 120k. My family needs a bigger house though so what do I do? Rather than spending another 200k on a new house, I sell my old house for 120k and buy next one for 200k making my new investment 80k. Whilst I recognise this isn't real life, getting back a % of your investment in a building seems a solid approach to me!