Fr. Z's blog contains this thread, one of the most thoughtful I've ever read with much enlightening discussion by priests.
http://wdtprs.com/blog/2007/11/from-another-entry-during-the-roman-canon-i-felt-intense-loneliness/
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Comments are closed on this thread, but I wanted to react to one specific observation. Priests commented on the loneliness of celebrating a Mass alone (how some will not even do it unless they can concelebrate). (The thread is not discussing that type of loneliness; this observation about celebrating alone was a tangent to the main discussion).
A small thought about the loneliness of a priest celebrating Mass alone.
When doing so I recommend that offering the Mass up for the intentions of the many millions who cannot attend a Mass at all is a great salve for the loneliness and the Holy Spirit heeds your offering on their behalf. This is true for both a Mass a priest celebrates Mass alone privately, or for those that are public but the priest experiences the loneliness of being the only celebrant.