We'll paraphrase Hawthorne here by saying "No (WO)man for any considerable period can wear one face to (her)self and another to the multitude without finally getting bewildered as to which may be the true."
There are many scenarios wherein you'll find it's easier to put on a particular persona to forge ahead. Whether it's your confident self promoting alter ego who does your interviews for you or the self-assured persona who knows her strengths and capabilities and will say she can do it first and learn how to later, it's a common and completely natural, if not encouraged, method of forging through uncomfortable situations. Many times it helps you get the job because you have the moxy or the skillset to get the job done well, and many times it helps an introvert work the room like the most natural extrovert.
Putting on a persona makes things easier, but it's also important to remember where the edge of the persona ends and the reality of you begins. So often we're lost in the blur. Sometimes it seems easier to stay in the persona because she gets what she wants, she's never down, she's confident and self-assured, she sticks up for herself and goes after what she wants, never let down by self-doubt or overanalysis, but just as you find yourself exhausted after a hard week, the persona too breaks down just as easily, if not moreso. It's not natural to always be 'on' - it's exhausting, it plays with your psyche in negative spiraling ways and it's just not physically possible. Think of it as working 18 hour days without sleep and only takeout for sustenance. Your body is not at its peak, you're tired and run down - probably have a cold- you forget easy things, you lose time in moments, and then hours until your body has had enough and shuts down to rehabilitate.
Wearing a mask to the world is a valuable tool for your career or to combat your introversion but there does need to be some separation between persona and reality.
Use it sparingly
While it's natural to believe that staying 'on' longer will help you get what you want faster, you're more likely to find you'll run out of gas too soon and still have plenty of road still to go. Use the persona only when required - interviews, networking, conflict resolution, times when shyness and self-doubt will harm you more than they will help you.
Take it off
Make sure that you have some separation between your home life and your goal life. Whether you're working towards a goal and need to be at peak performance constantly or your focus is your career, you can't reach peak performance if your too drained mentally, physically, emotionally to get out of bed. When you're at home, it's your sanctuary, there is no necessity for self promotion here.This is the place of couple snuggles (or dog snuggles) , DVD movies and messy bed hair.Take it off.
Never use the persona to fit in
In your personal life, it's especially hard to fit in with new crowds and if you're an introvert, your usual crowd is probably the dog and a couple of good friends. The persona should never make an appearance in your personal life (non-goal life). You can extract elements from it to diminish your tendency to overanalyse or doubt yourself or your partner in a healthy, mindful way but you should never be at a point where you've created a persona so strong that you can't keep up. This is where a lot of people fall into despair - depression brought about by constantly trying to be too much to too many people, trying to be a person that they think they're expected to be or wish they were when inside they're fighting to keep up and losing hope. You're amazing as you are, everyone else is taken, be yourself.
Be kinder to yourself
You're not there yet - you will be. You're struggling, but it's not forever. People around you believe in you so much more than you'd expect. They're so proud of you and your accomplishments even if you don't see them yourself. You are not your persona. You have all that strength and courage inside you all the time but out of humility, you downplay your accomplishments in reality, it doesn't mean they're not real or that you don't believe in them, it just means you're still focused on the road ahead. Take a moment every now and then to just reflect on what you've done and allow yourself to be proud