The way we wrote it we said that if n &lt; 2 return n 5 is definitely not less than 2 so we're going to go to the else part of the if clause or the else clause and say return fibonacci of (n-1) plus fibonnaci of (n-2)) so when I call this it's eventually be reduced to if you want to think about it that way, or simplified it would return, what is going to be the same thing as fibonacci of remember n was 5 so n-1 is 4 plus fibonacci of n-2, which when we ran the function n was 5 so 5-2 is 3 well these are just more function calls so now we are going to go again n is not 5, but 4 and 3 so let's try this out so over here n is equal to 4 n is equal to 4 so once again 4 is not less than 2, so we don't do this part we go to the else we then return fibbonacci(4-1) which is 3 so this is going to simplify to, or breakdown I should say to fibonnacci of 4-1 which is 3 plus fibbonacci of 4-2 which is fibonaacci of 2 so this right over here will essenitally return this and this over here on the right fibonacci of 3