The list of bone-headed things possible is . . . limitless lol. Most are merely temporarily inconvenient [like don't sneeze when pouring powder from the jug into your powder measure
], but double-charging a round is something to focus on avoiding.
Procedures (depending on how you reload) ranging from choosing powders whose normal loads nearly fill the case, through looking into each and every filled case before seating a bullet, to adding a powder check die on a progressive . . . these are examples of the multiple steps that prevent a potentially harmful situation.
Cartridges with no powder (squibs) may still occur - most of us have encountered at least one over our reloading career. The important thing here is that "click and no boom" at the range has real meaning . . . stop and check the barrel for a bullet lodged there by the primer alone.
But the best advice I can give is be very careful buying products based on reviews. Let's see . . . trimmers . . . presses . . . case gauges . . . let me focus on scales. I'm now on my 7th scale . . .
- the Lee Safety Scale that came with my first kit (works but an ergonomic PITA),
- a Hornady $30 digital (worthless),
- a $2XX Pact Scale/Dispenser (not nearly as consistent as reviews said),
- a $90 RCBS 5-0-5 (great beam scale; the only type of scale that can actually be calibrated at GRAIN levels by check weights rather than at 20/50/100 GRAM weights),
- a $125 GemPro 250 digital (not as useless as the Hornady, useful for setting your powder measure but cumbersome at best for trickling; eats batteries; sometimes flaky on its AC adapter; frequent drifting/inconsistencies)
- a $300 RCBS Chargemaster Combo dispenser/scale (better than the Pact; dispenser works fine with or without the straw; very often has more powder in the pan than the scale says.)
- a $550 FX120i is on it's way . . . the magnetic force restoration design should make it stable, sensitive and responsive enough for trickling . . . I'll let you know lol.
Point is, get a good beam scale . . . when your digitals go nuts the beam scale will ground you in reality. Work with it for a while because to really improve on that scale is likely gonna cost a *lot* more . . . and you don't want to get there in seven steps like I did.