What you need to know
Once growth leads to compounding growth and doubling it is an unsustainable trajectory because….
The growth during each new doubling time is greater or equal to all the previous growth combined.
For example look at the chart below of bacteria growth.
The same time it took to double from 1 to 2, is the same it took to go from 524,288 to 1,048,576!
And each time it doubles, the most recent double is greater (or equal) to all of the preceding growth combined!
The growth from 524,288 to 1,048,576 was more than all the growth plotted on the whole chart before that growth!
The growth in the last 1/2 an hour, from the 9 1/2 to the 10th hour mark was equal to all the previous growth from the beginning, the total 0.00—9.5 hours!

All that needs to be present is growth and time to get this type of chart!
Please watch this professors 9 minute lecture as understanding the exponential function is very important!
If you have time to watch the full lecture below.