A successful compile and upload proves that the toolchain transferred a program to the board; it does not prove that the program logic, wiring or power system is correct. This second part separates runtime faults from compile and upload faults.
The sketch uploads but appears to do nothing
Start with the Blink example. If Blink runs, the USB connection and basic board selection are probably sound. Add temporary Serial.print() checkpoints to find where execution stops. Check array bounds, pin modes, blocking while loops and conditions that can never become true.
Flash memory is not the same as SRAM
If a sketch exceeds flash capacity, compilation fails; it does not normally upload and then silently stop. A sketch that uploads but becomes unstable may instead be exhausting SRAM, corrupting memory through an invalid array index, or fragmenting memory with repeated dynamic String operations. On small AVR boards, store fixed messages in flash with the F() macro and prefer bounded character buffers where practical.
Serial-port conflicts
Close other serial terminals and programs that may hold the selected port. In modern Arduino IDE versions, the built-in Serial Monitor is managed with the IDE, but external terminals or another IDE instance can still block the port. Read the detailed console line before the generic “exit status 1” message.
Libraries and link errors
Install libraries through Library Manager when possible and confirm that the selected library supports the board architecture. Duplicate libraries with the same header name can make the IDE compile against the wrong copy. “Unsatisfied link” and stray .jar advice mainly belongs to legacy Arduino IDE 1.x plug-ins; for IDE 2.x, update the IDE, board package and library, then inspect the full compiler output.
Power and connected hardware
Test the board with external modules disconnected, then reconnect one module at a time. Motors, relays, radios and servos can cause brownouts or inject noise even when the code is correct. Use a supply with adequate current, common grounding and the proper driver and suppression components.
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