If you have played with a log fire then you will know that you need to add more wood to the fire before it dies down too much. In fact you need to add wood to the fire while it is nice and strong.
If you want the fire to grow stronger and bigger you need to add the heavier bigger logs while the fire is at its strongest. That way the flames will take to the heavy log and get into it by the time the current fuel starts to run out.
For a while after you have put the heavy log on the fire the fire will be a bit down. You have to be careful you don't add too many heavy logs at once or your dampen your fire too much and it will die or take a VERY long time to get back up again.
These thoughts came to me when I thought about how every time things are going really well something "happens"...
This is how I explain those "happening" things to myself.