I've found from my ongoing experience with Christianity that most groups (i.e. Bible studies, age-specific groups, location-specific groups, etc.) have a mentality suggesting that they think attendance is mandatory for a properly functioning Christian.  This belief evidences itself with statements like, "We have this group that meets every week; I can't understand why that person doesn't come."  While this belief is usually well-meaning and non-confrontational, it almost always looks and comes across negatively.  Many leaders, in their zeal to encourage attendance and build personal relationships with God (both are great things), overlook the fact that different people practice Christianity differently.  For one person, it could mean attending your Bible study.  For another person, it could mean not attending your Bible study and instead doing something else.  For the record, I would say most leaders acknowledge this fact and mainly want to encourage people to do something in their relationship with God.  But some leaders think their group is the group to attend, which makes it sound like it's the only way to get to God.  And this is obviously untrue.  Christian groups exist to bring people together and closer to God.  If a person doesn't see these effects in their life and wants to try something different, who are we (as group leaders) to stand in their way?