R. Bachya ibn Paquda states (Chovos Halevavos, Shaar Habitachon, Pesicha):
ואם יבטח על חכמתו ותחבולותיו וכח גופו והשתדלותו ייגע לריק ויחלש כחו ותקצר תחבולתו מהשיג חפצו
Taken literally, this implies that a person will never achieve success if he places trust in his own efforts.
Yet, isn't it commonplace for people to trust in their own efforts and still, at least occasionally, achieve success?
Rashi on the gemara in sanhedrin on page 26b explains that if one relies on one's own ability to accomplish something and doesn't recognize G.ods role in every action one performs, even in regards to Torah, G.od will make you fail.
מפר מחשבות ערומים - נותן להם מזונות ומבטל מחשבות מלבם שלא היו מניחין אותן לעשות תושיה ל"א מחשבה שאדם מחשב כך וכך אעשה כך וכך תעלה בידי מועלת להשבית הדבר שאין מחשבתו מתקיימת אפילו לדבר תורה כגון האומר עד יום פלוני אסיים כך וכך מסכתות בגירסא:
Regarding your question of exceptions to this statement — G.od works in mysterious ways. It could be something along the lines of how G.od doesn't punish the wicked right away in order to allow time for repentance.
To understand this point, you have to get to the root of what motivates us to do the things we do in life. Generally speaking, the flow of motivation in a neshama starts with desire, which activates the intellect, which activates the middot, which produce an action. So, everything starts with desire.
Desires come in different ranks. We have secondary desires, and primary desires. For example, the desire for money is not a primary desire. We don't actually want money (especially nowadays when it's just a piece of ugly paper or a number in an online bank account); it is a secondary desire: we want it for the sake of something else - comfort, safety, resources etc. This can lead to more secondary desires, until we get to primary desires. A primary desire is a חפץ.
There is nothing wrong with having a חפץ, as we generally do have noble desires, such as a desire to find someone else, to have a purposeful life, and to live a long productive life. Shaar Habitachon's purpose here is to help guide us in how we should approach the fulfilment of these noble desires. There's the intended way, and the wrong way.
The Pat Lechem indeed brings this point: we pursue our goals (secondary desires) in order to achieve our חפץ, our deep desire. He is basically explaining that the overall message of bitachon is that you should trust that your desire will be met and fulfilled by Hashem and following His ways alone (see chapter 2 and the 7 traits of trustworthiness).
If one is distrustful, and pursues achieving one's desire out of distrust that Hashem will take care of it for him, thinking that Hashem's ways will not get him what he wants, and therefore puts his trust in these pursuits instead, he will find that he never fulfills his desire in the end, guaranteed. As the passage continues: his strength will weaken, and his tactics will fall short of accomplishing his desire.
Money: This is one Rabbenu Bachaye himself brings further on (the example of the alchemist for e.g.). Our (holy) desire for money is rooted in our desire to be able to live a stable life that is tranquil, safe and that our needs should be met, so we can pursue our purpose in being created. If we don't trust that Hashem will take care of that for us, and we have to make sure of it ourselves by pursuing a career, under stress and anxiety, it means we are putting our trust in ourselves, and our own enterprise. We will end up working too hard, pursuing work that is not conducive to a tranquil and holy life, and having a life in constant anxiety that something will go wrong. In the end, even if we do achieve material comfort, we will not be able to actually enjoy it, and thus our actual חפץ will go unfulfilled. Only if we put our trust in Hashem, as the Rebbi explains, will we find those things.
Intimacy: People are born with a healthy desire for closeness and intimacy with someone else, which comes from when Hashem created the condition of it not being good to be alone, and it is a reunion between two halves of a soul (can't get more primary than that!). He commands us to channel this desire into marriage, and follow the laws such as controlling our eyes and heart, being shomer negia, refining one's character to make one a good spouse etc. Some people feel that if they follow Hashem's guidance in achieving the fulfilment of this desire, they will lose out, so they indulge in various degrees of promiscuity in their distrust. In the end, this path leads to tragic failure. They never achieve the true fulfilment of this holy impulse in their promiscuity, and the promiscuity itself damages and numbs them in many many ways, precluding them from fulfilling this desire even in the intended way.
