I am not outstanding
If we exclude the fact that I practiced a five-star manual, nothing about me was outstanding.
Not my stats
Not my physique
Not my skills
Compared to Kevin who had a system aiding him all the times, or the other main characters who had every resource they could ask for, I had nothing.
...I wasn't blessed by the 'plot armour' like the protagonists were
Everything I got was through shedding blood sweat and tears. I gained everything that I got by either putting my life on the line to get it or by sacrificing something important.
I had to make due with what I had.
When facing an opponent like Alex who had a lot more combat experience than I had, and moreover set a handicap to myself, I had to fight using everything that I had available at my disposal.
Thus I chose to fight a mental battle.
Since I knew that despite being weaker than me, Alex had more experience than me, I chose to beat him mentally.