McCollam has been squeezing $1 billion in costs from Best Buy in order to keep the electronics chain profitable. But the challenge has been to grow sales and market share at the same time — a formidable undertaking amid steep competition from online retailers such as Amazon.

What happened: After a rocky start to 2014 with disappointing holiday sales numbers, Best Buy has been building momentum on Wall Street throughout the year. Still, McCollam has been cautious in her statements to investors, calling out challenges such as a lackluster innovation cycle in consumer electronics and uncertain inventories for the iPhone 6 to keep expectations low. But Best Buy had a much better-than-expected third quarter, reporting its first sales gain in nearly two years.