Symmetry of i.i.d. continuous r.v.s problem, part 2

I have the following problem:

Athletes compete one at a time at the high jump. Let $X_j$ be how high the $j^{th}$ jumper jumped, with $X_1, X_2, \dots$ i.i.d. with a continuous distribution. We say that the $j^{th}$ jumper sets a record if $X_j$ is greater than all of $X_{j - 1}, \dots, X_1$.

2. Find the mean number of records among the first $n$ jumpers. What happens to the mean as $n \to \infty$?

The solution provided is as follows:

By linearity, the expected number of records among the first n jumpers is 􏰇$\sum_{i = 1}^j = 1/j$ which goes to $\infty$ as $n → \infty$ since the harmonic series diverges.

I understood everything except for where the 􏰇$\sum_{i = 1}^j = 1/j$ came from. I would greatly appreciate it if people could please take the time to explain this.