The story of Sage Vishvamitra is known to us all.
A king called Trishanku requested Vishvamitra to send him to heaven with the physical body. When the king told Sage Vishvamitra that even his Guru, Sage Vashista, said he could not send him to heaven with the physical body, Sage Vishvamitra immediately said he would fulfil his wish to go to heaven
Now Vishvamitra was least interested in sending Trishanku to heaven. He undertook to send him only because he wanted to show that he could accomplish something that even his Guru could not!
Likewise, a disciple or an aspirant in the spiritual path may face pitfalls like Vishvamitra because of lust (like how the sage lost his penance due to lust on Menaka), of anger (like the sage's encounter with Rambha), or because he wanted to exhibit his prowess (the sage trying to straighten a hunchback and losing all his penance).
All of these are most dangerous pitfalls that throw the aspirant into the darkest abyss!
But, the worst pitfall in sadhana is trying to compete with one’s own Guru in the despicable display of one-upmanship with the divine Satguru himself!