So you're basically saying a person needs to accept death but dying too to be at peace with suicide.
My main point is that survival instinct is not worth considering in the given context. Explaining failed attempts through survival instinct is too primitive, counterproductive, and likely to be wrong (if we take the differences between reflexes, instincts, and learned behavior into consideration). It doesn't provide us an adequate detailed picture of what actually happens, and it doesn't suggest any good solutions, since survival instinct is commonly viewed as just a magic force that prevents you from killing yourself somehow.
There exist at least three demotivators that can work against suicide: a desire to live and enjoy some things in the life (that can coexist with the desire to die due to the negative aspects of life), unsureness that the chosen suicide method is sufficiently effective and worth using, and intolerance to discomfort. The motivation to commit suicide with the chosen method has to compete with these demotivating factors, and it should be stronger.
A competition between opposite motivations is common. If you're a smoker and you want to stop smoking, your logically reasoned motivation to get rid of the unhealthy habit will compete with the motivation to get rid of the discomfort caused by withdrawal. Most people probably wouldn't associate such a discomfort with the survival instinct, because it motivates towards a self-destructive behavior which is "anti-survival" by its nature. The concept of survival instinct is flawed, it doesn't explain why a discomfort can be destructive in some cases.
Many suicidal attempts were aborted because the actual perceptions happened to be worse than anticipated. The influence of unusual perceptions and possibly altered state of consciousness could make it difficult to analyze the situation logically. In such cases, the decisions are made based on intuition, which may suggest that the whole plan is likely wrong because some part of it doesn't match the initial expectations. This pattern of intuitive thinking is not necessarily instinctive, it could be learned.
You probably can prevent undesirable intuitive decisions via planning and reaching acceptance of the worst scenarios beforehand. On the other hand, belief in difficult-to-overcome survival instinct can be a psychological barrier on itself, which can deprive you from confidence and belief in your abilities. Thinking of suicide as a hard procedure doesn't make you better prepared to it.