Everything that is not an elementary necessity, such as food and water, can be found within.
Many things in which we pursuit, can be found within us, making many of our external pursuits, unnecessary, and at times, tiring and frustrating.
While we cannot find a sports car within ourselves, we indeed can stimulate many experiences that are usually gained externally, through mental training. We can stimulate the feeling of driving in a sports car, using only the mind.
This is why those who may be in esoteric countries, where many of the luxuries we first-world members have are missing, may be happy just like us, or even more than us - some of them may obtain a mindset that keeps them happy despite of their financial deprivation. You could literarily be in an empty room and be extremely happy, while another person could be in a luxurious penthouse and suffocate.
The roots of our mental state lies mainly within our specific mindsets. External stimulation may be inferior to our mindsets if we are to adopt or create a mindset that can be used to surpass said stimulation.
It is a matter of introspection, of listening to your thoughts, inspecting them and altering them in any way you wish. You are not your thoughts, nor emotions. While you cannot choose them directly, you can influence them directly to indirectly choose your thoughts and emotions, making you a possible dictator of your own Internal World.
It can be comparable to trains and those responsible for the alteration of the railroads. Your thoughts and emotions are those trains, and you cannot control them. What you can control, in the comfort of your station, is the way said trains would go. While you cannot command the trains and their drivers, you can control the railroad networks, narrating the trains in any way you wish.
The metaphorical station you’re in is so invulnerable, no external stimulation can go inside of it unless you choose it to do so. Thus, even in the hardest of situations, you still can preserve or alter the railroad network of the trains, making your mentality a potential source of autonomy and endurance. Even if you are to experience something difficult, you nevertheless can choose how to view it and relate to it in any way you choose.
The frustrated person is deceived. They are unaware of the inner potential that lies within them, to become more self-sufficient and stronger through the training of the mind. They may see themselves as victims to external circumstances, which could possibly lead them to a pessimistic view towards life in general.
The wise person, however, knows that they are the horse driver and not the horse themselves. They differ between the screen and the person that watches the screen and holds the remote control. They know that they will hear loudly if they raise the volume, and see darker or lighter if they change the colors of the television. Perspective is a matter of either adopting or creating, and accepting or rejecting. That’s how illusions work, and perspectives are a component of them.
Either way - adopting or crating and accepting or rejecting - it is all a matter of preference and influence. The influence is the stimulation received, and the preference is the way you let said influence affect you. How much you let stimulation affect you, is of your own choosing, even if there are more factors involved. Even if you believe you are the victim of external circumstances - the belief itself is, too, of your own choosing.
The more you will understand this insight and use this insight to design your perception of reality in accordance to your own choosing, the wiser you will become.