Resistance to a subliminal is when some part or parts of your awareness is at odds with the new programming a subliminal is attempting to install, and tries to reject, avoid, stop or otherwise refuse it.

Resistance to subliminals can be complex and there are several types. In some cases the resistance is conscious, and is overcome by a willing subconscious, or consciously thwarting an unwilling conscious. In some cases, it is both conscious and subconscious. In some cases it is subconscious only.

It is very difficult to consciously thwart an unwilling subconscious because the conscious is very limited in comparison. This rarely works (about 10% of cases), but is possible.

If resistance is both conscious and subconscious, it will be almost impossible to consciously overcome by oneself until the resistance of one or the other is overcome, or help is gotten from a skilled mind programming operator using NLP, hypnosis, etc.

If resistance is subconscious only, it is challenging to overcome, but one can use conscious actions to succeed, such as subliminals, affirmations, hypnosis, etc.

Resistance to a subliminal is usually very difficult to overcome if the root cause (nearly always some sort of fear) is not dealt with first. It is possible, but requires a different approach, a different style of mind programming, or significantly more time.

A different approach usually means that you deal with the cause of the resistance, and then worry about what's being resisted. In other words, you will be working on fear first, which is almost invariably the cause of the resistance, instead of whatever else you might have been trying to accomplish that was being resisted.

A different style of mind programming is going to be something like hypnosis or NLP instead of subliminals. Something the conscious mind can see and understand better and fear less to resist less. Again, it boils down to dealing with fear.

More time, of course is the approach of the wind wearing down the mountain. Given enough time, all things change, even by the light touch of the wind.