On Monday, The We Company confidentially filed to go public and Uber kicked off its investor roadshow ahead of its public market debut. Both companies were "unicorns," privately valued above $1 billion. 2019 has already been a blockbuster year for unicorn IPOs with notable exits from rideshare company Lyft and video conferencing startup Zoom. Several companies currently eyeing a public offering stayed private longer than other companies in the past, netting massive returns for investors that took early stakes at lower valuations.