you do not own your thoughts, you host them.
Thoughts are like frequencies picked up by a radio station.
When a thought comes to mind, it mysteriously presents itself as inborn.
However, in fact, any thought that comes to mind always has an external source or trigger - an external cause that you may not be consciously aware of.
It is like when you suddenly start singing a song only to discover that it was playing on your neighbor's TV at the same time you were singing it.
You may not be quite aware that your hearing could reach as far as the building across, but your subconscious mind picks up sounds and visuals from distances that are way beyond your conscious circle of reach.
The mind, being coded by The ONE (call this ONE God or Absolute Unity), has an inclination to frame images numerically by way of simulating infinite unity through a finite one.
Call this mind tendency self-reflection (the mind mirroring The Creator in him). Accordingly, the mind acts like a creator that is capable of providing any image a form of presence by framing it as one.
A framed image in mind is referred to as a thought. However, the mind in fact is only hosting this image within a numeric frame and not creating it.
The Mind is not meant to exhaust its infinite state-of-unity to those finite numeric entities (thoughts). Thus, the mind is granted the power to negate thoughts (drop those frames and release the images trapped inside them causing them to melt back into the black hole of unconsciousness or infinity). The mind does so by way of denying those images' similarity to the original unity that constitutes its default boundless nature.
This act of negation can be thought of as a form of worship so to speak, because its underlying logic entails an affirmation to the existence of no unity comparable to God's Unity.
Accordingly, negative thoughts acquire their negativity not by virtue of any particular content inside the frame, but rather due to the nature of the frame itself which attempts to claim a fake unity and presence on the expense of the authentic unity.
Even more, there is no negative content per say, there's only a 'no' attached to a meaningful image in mind. In other words, when you're afraid of unhappiness, you're actually only imagining happiness being negated and that's how the mind conceptualizes unhappiness.
Thoughts make you believe you're responsible for their blasphemous weight of presence, and that you have no choice over accepting or renouncing such responsibility.
From here, its important to understand that you are not the creator of those thoughts (however negative they are), you're only the host; and the host has the right to kick the visitor out if the visitor threatens his sovereignty and well being.
YOU ARE NOT THE CREATOR OF YOUR THOUGHTS?!
As much as this fact may break your ego, it mends your soul. You are not responsible for your negative thoughts. You are only responsible for any negative thought to the extent that you think you are; and renouncing responsibility is as simple as dropping the thought.
Negative thoughts feed upon the host's presence and energy. They are nourished and solidified through his physical expressions and actions in space and time, stirring turbulence, breaking a harmony or a rhythm; and the whole process becomes like a vicious circle. More turbulent expressions and actions, trigger more negative thoughts.
Its thus important to understand that you have a Choice over a given thought's presence in your reality. You can either renounce responsibility for that thought and turn your eyes away from it - preventing it from materializing in your world, or keep looking at it and looking, sustaining it with power and energy, allowing it to sneak its way into your expressions and actions - setting the stage ready for further negativity to take over your world.