Different decompositions of the string in the pumping lemma proof
Here is the statement of the pumping lemma:


  If $L$ is a regular language then there exists an integer $p$ such that every word $w \in L$ of length at least $p$ has a decomposition $w = xyz$ such that (i) $|xy| \leq p$, (ii) $y \neq \epsilon$, (iii) for all $i \geq 0$, $xy^iz \in L$.


Here is the contrapositive, which is how you usually apply the lemma:


  Suppose that $L$ is a language such that for every $p$ there exists a word $w \in L$ of length at least $p$ such that for every decomposition $w = xyz$ satisfying $|xy| \leq p$ and $y \neq \epsilon$, there exists $i \geq 0$ such that $xy^iz \notin L$. Then $L$ is not regular.


When you apply the lemma to show that a language is not regular, you have to consider all possible decompositions satisfying $|xy| \leq p$ and $y \neq \epsilon$. For each of them you need to find an $i$ such that $xy^iz \notin L$.