There is a reason we have expressions like "Good Time Charlie."

Relationships based solely on shallow, easy and fun experiences tend to be weak relationships that aren't likely to withstand the inevitable storms of life.

On the one hand, you don't want the person to be the primary source of trouble in your life. On the other hand, if there isn't some kind of inherent friction, the odds are good that everything will fall apart at the first strong wind, so to speak.

Strong relationships tend to be relationships where the personal bond is sufficient to withstand some stress. This is very often due in part to inherent friction within the relationship.

People who need to work at it and actually do tend to have stronger relationships than those with so-called chemistry. Relationships that "start with a bang" often soon end with one.

Well, maybe not "Relationships with intense difficulty", but it's a very common and very naive assumption that the perfect person for you will "just work" and there will be no fights and no difficulty. Loving someone is a lot of hard work - and it's extremely rewarding. Teenage relationships where everything "just works" and everyone is in bliss tend to end with a lot of tears.

Anyways, yes, it's not a set-in-stone rule - but typically, anything that's extremely easy also has a disappointing side. The best stuff in life takes work.