What is one of the major obstacles a spiritual aspirant must overcome?

You should avoid the difficult obstacles in the path of meditation, viz. anger, pride, conceit, the tendency to discover the faults of others, mischief, etc. These operate even subconsciously, just like the currents in the depths of the ocean. Spiritual aspirants must be vigilant not to lose their temper on even small things, for that will block their progress. They must cultivate love toward all, and gentleness. Then, undesirable habits will fall away from them, since anger is the parent of all wrong behaviour. Anger can turn any person into bad ways, any moment, and in any form. So it should be sublimated first by systematic effort. Spiritual aspirants must gladly welcome the announcement of their defects by anyone; indeed, they must be grateful to those who point them out!

– Dhyana Vahini, Ch 14.