I think that there are two primary factors and both are related to the individuals more so than the relationship:
The most present factor is often one or both individuals not being ready to be in a relationship. This takes on many different forms. One of the most prominent is gaps of maturity/capability. There was a research study that showed the number one most influential factor on women immediately swiping left on a dating profile is when he states he does not drive (Ogas & Gaddam, 2011). While competence is related to a woman's attraction, this manifests more into an immediate red flag of what expectations could look like in a relationship. It is the "I want to be a girlfriend, not somebody's mom". When we see age gaps in relationships it is usually due to chronological age not making individuals automatically be peers. Alternatively, this can manifest in different types of maturity gaps as well. For example, can the individual control their emotions or do they require their partner to provide them comfort? Does the individual have the autonomy to engage in entertainment separate from their partner? When one or both individuals are not yet ready to be in the relationship, what often ends up happening is a fatigue followed by loss of interest. That being said, there is no universal bar of maturity. The expectations are relative of the partners. Two teenagers likely have far less focus on emotional stability expectations when neither of them have fully developed brains yet.
The second factor is disagreement over core values. Most healthy couples are able to overcome most challenges as long as they are in agreement and consistent on these core values. If both people genuinely feel the same over core topics, disputes otherwise can usually be resolved. If both individuals have equitable stances on things like what defines cheating, for example, it's very rare disagreements otherwise end the relationship. The catchall term of "communication" is only half the battle. It's being able to identify and articulate what is significant in these spaces and determining if these stances are shared. If they are not, the relationship is often fated to fail.
A relationship's foundation can absolutely be assessed at the start. While it does necessarily guarantee anything, most relationships that have equal partnerships and shared core values tend to have the highest levels of resiliency.
Ogas, O., & Gaddam, S. (2011). A billion wicked thoughts: What the world's largest experiment reveals about human desire. Dutton/Penguin Books.
