Been doing some light research on string theory. initially my understanding veered towards general relativity being encompassing and quite detailed with its angle on doing differential geometry on a curved manifold, leaning on the fundamental machinery of Riemannian geometry.

The usage of tensor algebra and calculus did seem intimidating at first, but just like mastering any other skill, it gets relatively simple with persistent understanding. In fact, even a complex solution like Schwarzschild's celebrated black hole equation can be approximated in under a page, or even mentally (once your mind is well-trained obv)

Acknowledging the century old science or mathematical roots tracing back to the mid-19th century does help us comprehend it better but there's no denying the complexity of certain oddities (like binary black hole mergers, anyone?)

However, an adventure into string theory made me realize that general relativity can be a kindergarten level of understanding when compared to the former's vast and complex framework. For string theory, you're merely scratching the surface if you're familiar with just general relativity.

String theory demands a thorough knowledge base in topics beyond general relativity, such as Lagrangian and Hamiltonian mechanics, quantum mechanics, classical and quantum field theory, gauge theory, the concept of supersymmetry, renormalization theory and an understanding of quantum gravity puzzles. This seemingly endless list (which btw is 100% incomplete) merely prepares you to embark on the journey of exploring the theory, it doesn't even get you halfway. Moreover since string theory is still an "open-case", its lack of a solid groundwork or unanswered questions make it more convoluted and far less polished than general relativity.

Basically the main issue is the vast number of unknowns, but then again that is what lured me to string theory in the first place.