This question is a very fundamental one, which cannot be answered in the same way for everyone. Because: there are two completely different ways to go on pilgrimage.
Pilgrimage alone
If you pack your rucksack and set off in the hope of finding answers, you should definitely go alone. Those who go on a pilgrimage to learn something about themselves, perhaps to find more of themselves, should go alone. Those who want to overcome their fear of being alone with themselves should go alone. But also those who go on a pilgrimage to become a little more courageous, who want to face a challenge, who want to grow in a little adventure and prove to themselves that they can do more than they think they can, should definitely go on a pilgrimage alone.
Pilgrimage in pairs
For those who use pilgrim paths for long-distance hiking, for those who are primarily looking for a sporting challenge and want to take advantage of the good infrastructure and good signposting, running in pairs is the better option. Because it is always cheaper to stay in double rooms and in the evening it is nice to have someone to keep you company during dinner and with whom you can exchange ideas about the day.
Help, alone is stupid!
Nobody has to be afraid of getting lonely on the way. Even if you are rather introverted, you will always find company as a solo pilgrim. I have always experienced pilgrims (whether hostel sleepers or hotel sleepers) as open-minded people.
It is precisely because so many are on their way alone that in the evening they quickly form loose groups that meet in ever new constellations at the various destinations, depending on the individual stage length. If you know beforehand that you would like to make contacts, you should take this into account when planning your trip and choose the inland rather than the coastal route for the Portuguese Way of St. James.
Moreover, we live in a time in which it is possible to keep in touch with friends and families at home from anywhere at any time. So even if you think all other pilgrims are stupid and prefer to keep to yourself – you are not in a Tibetan monastery without mobile phone reception.
What if I want to stay alone?
I don’t find it at all reprehensible to escape the pilgrim community and do one’s own thing. Not getting to know anyone, preferably not even seeing other pilgrims. Everyone should use the way for himself in the way that is right for him. And especially when you go hiking in order to be able to deal with yourself in peace, it can be very helpful to avoid human contact as much as possible.
The best way to do this, of course, is to travel at less popular times. For the Portuguese Way of St. James, the less frequented coastal variant is also recommended. Especially from Spain it gets very lonely there, because this route is not mentioned in the usual pilgrim guides.
The time of day at which you set off on your hike also plays a decisive role: because hostel sleepers are thrown out of their hostels at unholy times, they are usually on the road very early. And because most pilgrims are “real pilgrims” and the starting points of the stages are the same for almost everyone, the number of fellow pilgrims is reduced enormously if you start at ten or eleven o’clock and arrive late at your destination.
For “luxury pilgrims” this is no problem, the hotel is reserved and waiting for you and the towns are usually so small that you can easily add some sightseeing, even if you arrive at 6 pm.