Haskell's lazy evaluation means the order of operations is not guaranteed, making side effects like `print` statements unpredictable. This forced the language to be pure by default. Conversely, OCaml's strict, predictable evaluation order made it easy to incorporate I/O and side effects, allowing it to be impure by default.

Instead of viewing velocity and dependability as a trade-off, engineer systems where the easiest, most automated path is also the safest. This "pit of success" makes the right choice the default for developers, aligning speed with reliability.

This approach contrasts with imperative languages where computation proceeds by mutating a state over time (e.g., a running total). Functional programming is more declarative, like a mathematical expression or a spreadsheet cell that calculates its value based on others, making it easier to reason about.

A severe physical limitation can be an unexpected catalyst for growth. Boris Cherny, after breaking both arms, was forced to find languages with fewer keystrokes. This led him to discover the power and efficiency of functional programming, fundamentally improving his coding approach.

Most compilers use complex, untyped intermediate representations. GHC desugars Haskell into a tiny, statically-typed language called Core. This allows a type-checker to run after each optimization pass, immediately catching bugs in the compiler that would otherwise manifest as cryptic runtime segfaults in the final compiled program.

In imperative code, functions can silently read or write shared global variables, creating invisible and dangerous dependencies. Functional programming forces these interactions to be explicit (e.g., through function arguments or monads), encouraging a more modular and less coupled design that is easier to reason about and maintain over time.

To mitigate the risk of expensive physical failures, hardware control software company Revel developed its own programming language. A core feature is that if code compiles successfully, it is guaranteed not to crash at runtime. This design choice eliminates a common source of catastrophic errors in hardware operation.

The power of monads isn't just to sequence side effects, but to treat those entire sequences as first-class values that can be passed, stored, and reused. Unlike in C, Haskell's `do` notation bundles I/O operations into a value (e.g., of type `IO unit`) that can be composed and manipulated like any other data.

This phrase can be read two ways: "avoid success, whatever the cost," or "avoid the kind of success that comes at the cost of your principles." For Haskell, it meant not compromising core ideas for mass appeal. It also warns that too many users can create immense backward-compatibility pressure, hindering future innovation.