Giving and receiving true pleasure; That hits it on the head. You're absolutely right, not everybody is set up for everything. If the cock is sensitive, it can be even challenging to get a regular blowjob. It is also the shape of the cock that greatly influences a successful encounter. Curved, especially upward or slightly sideward, can be daunting for the sucker, and even slight position adjustments don't fully compensate for a "forced" fit, which can cause discomfort on both sides. It is basically a requirement to find the "perfect match" for both anatomies, so it will truly feel spectacular. Thick girth is more difficult to accommodate due to physical limitations of the recipient, there are bones and other fixed structures involved that cannot be stretched or trained, even if the desire is strong. Finding out what works and doesn't work is a big part of all this, for all involved. Keeping an open mind and occasionally giving this another shot might just reinforce the aversion, but there's still the slight chance of encountering a new and awesome level of satisfaction.