We know we are to separate ourselves from worldliness, for the Scripture says, "Be ye not conformed..." We know we are to have seasons of retreat for prayer and fasting. We know it is wise to pull aside for quietness, reflection, meditation and study.
However, I believe Proverbs 18:1 is talking about something else. The key is where the Scripture says, "he breaks out against all sound judgment." It seems to indicate an attitude of refusing to listen to wise input from others.
Sometimes, people simply do not want any other voice than their own speaking into their lives. They only value their voice. Proverbs 18:2 says, "A fool takes no pleasure in understanding, but only in expressing his opinion."
Sometimes this happens out of sheer pride. Some feel that no one is as smart as they are. Some feel no one is as good as they are; they are the only ones getting it "right" is their view.
Sometimes this happens out of pain. Some feel no one understands their pain, or can speak into their sorrow and troubles.
Sometimes people separate themselves out of apathy. They simply do not care.
According to several commentators and translators, Proverbs 18:1 is a tough verse to translate. It may be one of those Proverbs that is a "riddle" (1:6) and meant, as is the Eastern custom of riddles, to make us think without having a definite answer. And, that is a good thing, to think and probe our motives, to consider the depths of hearts and to see the Lord's face and wisdom in the issues of life.
What makes you run into solitude?
Is it to renew? To seek God's face?
Is it to pull away from people?
Is it out of pain and sorrow?
Is it out of pride or superiority?
For sure, and not to belabor it, isolation has a benefit, but that benefit will only be gained if it has begun in the right motive.