Reading CLRS analysis of hashing with chaining
I assume that you are talking about the hash-table that uses an adjacency list for the elements that have the same hash key (hash table using chaining). Let's look at a very simple example. 

We have a hash table such as the following:

key : like list of elements
1   : x_11 -&gt; x_12 -&gt; ... -&gt; x_11000000 -&gt; NULL  // 1000000 elements
2   : NULL                                       // 0 element
3   : x31 -&gt; NULL                                // 1 element


If you look at keys 1 and 3, which one is more likely to be visited? The answer is 1, because it has more elements than all other lists. Therefore, we are more likely to find the mysterious element in 1's linked list.