This is because the nth term is found by adding the previous two terms
F(n) = nth term
F(n-1) = term just before the nth term
F(n-2) = term before the F(n-1) term
F(n) = F(n-1) + F(n-2)
We can re-index values of n to say this equivalent statement
F(n+2) = F(n+1) + F(n)
Based on either equation mentioned, adding F(51) and F(52) will get us F(53). In other words, the 51st and 52nd terms add to the 53rd term.