Stress hard on my soul
And shackle my mind, making my heart cold
And my head hot, cause's bread not, coming in and I'm
Losing my cool,

from Elzhi (Ft. Fes Roc) – The Science Lyrics on Rap Genius

Meaning

The challenges of every day life and not making enough money are weighing heavy on El and strongly stressing him out, confusing him..
Then, by making his heart cold and his head hot you could take it as he’s starting to become ruthless.. as in he would do anything for money. Cold hearted people are typically known to not care for others feelings, just want their own desire no matter the cost. Hot headed would imply he’s not thinking rationally.. he’ll just do things on a whim. It also tells us he’s angry. The combination of being cold hearted and hot headed are quite formidable and dangerous to others standing in his way.

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