This qualitative research article is based on interviews with 20 participants to a low back pain rehabilitation program in a Swiss hospital. It shows that, in the absence of the obvious cause that can explain pain, patients construct their own interpretations and explanations in order to give meaning to their experience. Their explanatory models mainly include the lifestyle and the physical aspects related to the body function, what leaves little room for the psychosocial component. Their interpretation is consequently discordant with the current medical approach, which considers that chronic low back pain results from bio-psycho-social factors. This discrepancy implies negotiation between patients and professionals about the objectives to achieve in order to treat pain.